In a conventional art, as a linear motion guide device of this kind, the same applicant as that of the present invention had already proposed a linear motion guide device assembled with a chain for holding plural rows of balls in which two ball rows are held by one ball chain (see Japanese Patent Laid-open Publication No. HEI 5-126149). That is, this linear motion guide device is provided with a track rail and a movable block mounted to the track rail to be movable through a number of balls.
The movable block is composed of a movable block body having a loaded ball rolling groove corresponding to a loaded ball rolling groove formed to the track rail and a non-loaded ball return passage formed in parallel thereto and end plates disposed to both ends of the movable block body and adapted to form an endless ball circulation passage communicating the loaded ball rolling groove and the rolling member return passage.
The balls constitute two ball rows separated from each other with a predetermined distance and in parallel to each other, and these two ball rows are held by a plural ball row chain to thereby circulate in the endless circulation passage. The plural ball row chain has a structure composed of a flexible connection member disposed between two ball rows and spacer members located at both side edge portions of the connection member and adapted to be inserted into balls of the respective ball rows so as to smoothly perform the circulation of the balls.
However, in the conventional technique mentioned above, because the plural ball row chain is formed from a belt-shaped member having a cut end portion, the end portion of the ball chain hangs down at a time when the movable block is removed from the track rail.
In a state that the end portion of the chain hangs down, when only the movable block is assembled with a table or the like, the hung end portion of the chain may be engaged with the table, which may result in that the plural row ball chain is withdrawn from the movable block or, otherwise, is twisted or clamped thereby, thus providing a troublesome working problem and, in a certain case, damaging the ball chain.
Further, although the respective ball rows are circulated in alignment through the spacer members of the ball chain, the smooth circulation movement of the ball may be blocked in the presence of stepped portions, caused by, for example, assembling error, at connection portions between the loaded ball rolling groove and a direction changing passage inner periphery guide portion and between the direction changing passage and the non-loaded ball return passage.
Furthermore, there may easily be caused a positional error of an outer periphery guide portion with respect to the inner periphery guide portion of the movable block body by an assembling error at the time of clamping the end plates or self-deformation of the end plates. Since the end portion of the outer periphery portion approaches the loaded ball rolling groove of the track rail and constitutes a scooping portion for scooping the balls, it is necessary to make such error as small as possible in order to perform further smooth circulation of the balls. Particularly, in the case of two ball rows, it is necessary to exactly set a pitch between the direction changing passage outer periphery guide portions of the end plates corresponding to two rows of loaded ball rolling grooves. However, in the conventional technology, the end plates have been formed through a molding process, so that it is extremely difficult to exactly perform a molding working because of deformation due to burr of a material in the molding process, and there is a limit for enhancing a mounting performance.
The present invention has been proposed to solve such problems in the conventional technique mentioned above and an object thereof is to provide a linear motion guide device having a plural ball row chain capable of being easily assembled and achieving an improved circulation of balls.